Thin films of lanthanum-doped lead titanate for use in pyroelectric detectors were deposited on Si wafer system substrates by an RF magnetron sputtering method. Deposition was from a ceramic target with excess lead using Ar plus N2O sputter gases. The film structure, composition and electrical properties were examined as a function of substrate temperature during film deposition, Tsub, from 600°C to 750°C. Dense, featureless film cross-sections existed up to Tsub=625°C, while vertical columns, indicative of crystalline material, were present from Tsub=650°C upwards. At Tsub=600°C films were amorphous, but from Tsub=625°C upwards a highly crystalline perovskite phase was found. The tetragonality was very small, c/a˜1.006, indicating the existence of a pseudo-cubic structure. Compared to the idealized chemical formula, Pb1−xLaxTi1−x/4O3, films produced at Tsub<650°C or Tsub>700°C were Pb deficient, while only in the very narrow 650–700°C Tsub range was near-stoichiometry obtained, with a slight lack of Ti. The substrate temperature during deposition is apparently a critical factor in obtaining stoichiometric films. The La content with respect to Pb was 9.5% which would be expected to yield a reasonably tetragonal crystal structure in bulk material, however stress due to the substrate may account for this discrepancy. The relative permittivity, εr, showed a sharp transition from ˜50 at Tsub=600°C to 450–550 between 650°C and 750°C. This behaviour parallels both the microstructural and crystal lattice changes from amorphous to perovskite material. Even though on polycrystalline underlayers, pyroelectric activity, p, was measured on as-deposited films, the polarization being directed into the substrate and a peak of 1.2×10−4Cm−2K−1 appearing at Tsub=700°C. After DC thermal poling, at 100°C with 8V for 20min, p increased dramatically, with Tsub 700°C and 725°C films exhibiting p=2.0×10−4Cm−2K−1. The peak in the poled p value corresponded to the maximum found in the crystal tetragonality and agrees with increasing p as polarization increases from a cubic to tetragonal structure.